1. Field of the Invention
The present invention relates to a wire bonding method and more particularly to a method for correcting the ultrasonic oscillation output of a transducer.
2. Prior Art
Japanese Patent Application Laid-Open (Kokai) No. 2-119154 discloses one of ultrasonic oscillation systems for transducers used in wire bonding.
In this system, a constant ultrasonic oscillation is obtained under the same bonding condition regardless of differences in the characteristics of the transducers used. A correction method for obtaining such a constant ultrasonic oscillation utilized in this system will be described with reference to FIG. 2.
As shown in FIG. 2, electric current 1a which is fed back from a transducer 1 is amplified by a current amplifier 8 of an ultrasonic oscillation control circuit 4. The transducer 1 has a bonding tool 2, and a bonding wire 3 passes through the bonding tool 2. The resulting amplified current 8a is converted into digital current data 10a by an A/D converter 10, and this data 10a is inputted into a microcomputer 5.
The microcomputer 5 calculates differences in the characteristics of the transducer 1 and outputs ultrasonic oscillation output data 5a to an output control circuit 11. This output data 5a has been corrected so that an ultrasonic oscillation, that is the same as one which is established by manual input data setting or by data transfer setting, is obtained.
Electric current 8a and output voltage 7a of a power amplifier 7 are inputted into a phase detection circuit 9. The phase detection circuit 9 reads the voltage phase and the current phase and outputs a voltage 9a (which is proportional to the phase shift) to an ultrasonic oscillation circuit 6.
The ultrasonic oscillation circuit 6 outputs an ultrasonic oscillation voltage 6a to output control circuit 11. The ultrasonic oscillation voltage 6a performs ultrasonic oscillation in which the transducer 1 synchronizes on the basis of the voltage 9a that corresponds to the phase shift. The output control circuit 11 controls the ultrasonic oscillation voltage 6a, which is inputted from the ultrasonic oscillation circuit 6, in accordance with the ultrasonic oscillation output data 5a and outputs the voltage to the transducer 1 via the power amplifier 7.
Thus, since the voltage applied to the transducer 1 is corrected according to the output voltage 7a, equal oscillation amplitude is obtained even if the oscillation characteristics of the transducer 1, that includes a transducer supporting member, is different. Accordingly, as long as the data input setting is the same, the same or equal bonding strength can be obtained in different wire bonding devices. Furthermore, since the bonding can be done evenly to any workpiece, there is bonding interchangeability, and data transfer between different wire bonding apparatuses becomes possible.
Thus, the above-described prior art discloses a method to correct the ultrasonic oscillation output in order to correct the differences in the transducer characteristics. However, no particular consideration is given to timings or when the ultrasonic oscillation output correction should be performed.